Estimation of vitamin B12 (hydroxocobalamin) in proteolysed liver extracts.

The stability of hydroxocobalamin to ascorbic
acid-sodium ascorbate (AAM) in the
presence of varying concentrations of iron
has been studied. Iron In concentrations
higher than 3-5 ['g./ml. prevents the destruction
of hydroxocobalamin by AAM to varying,
extents, 100 per cent protection being, attained
at 32 l~g,. level. At levels less than 1·5 ['g.,
iron does not exhibit any protective action.
Cyanocobalam.in is not destroyed under the
above conditions. Hydroxocobalamin present
in proteolysed liver extracts couId be selectively
destroyed by treatment with AAM if
the iron content of the extract is adjusted to
about 1 ['g./ml. by suitable dilution of the extract.
Based on the above findings, a method
for the determination of hydroxocobalamin
content of liver extracts has been developed.
The results of analysis of a few samples of
proteolysed liver extracts indicate that about
50-60 per cent of the vitamin B,. activity of the
extracts is due to hydroxocobalarnill.